BRALOWER, T. J., Department of Geology, University of North Carolina, Chapel Hill, NC; and W. V. SLITER, USGS, Menlo Park, CA

ABSTRACT: An Integrated Cretaceous Calcereous Nannofossil and Planktonic Foraminifer Biostratigraphy

Original zonations for Cretaceous planktonic foraminifers and calcareous nannofossils were developed over 20 years ago in northern and southern European land sections. These zonations have been modified since in part by the addition of subzones, however, the resolution remains low, averaging 1-2 m.y. At the same time, there have been advances both in techniques and taxonomy. Continued operation of the Deep Sea Drilling Project and Ocean Drilling Program has led to recovery of new Cretaceous sections, including critical sites from high latitudes. Many of these sections are expanded relative to those in which original zonations were developed. Time is ripe therefore for the development of zonations of both planktonic foraminifers and nannoplankton offering higher resolution.

We have derived a higher resolution, integrated nannoplankton and planktonic foraminifer biostratigraphy for the Cretaceous Period. This biostratigraphy is based upon a literature survey of numerous DSDP/ODP and land sections as well as our own reinvestigation of several of these sequences. The sites included are from high-, low- and temperate latitudes, and from all the major ocean basins, allowing differentiation between events which are globally applicable and those which have a regional or latitudinal context. We have concentrated on increasing the resolution of current nannofossil zonation schemes which was somewhat behind those of planktonic foraminifers. We also propose an informal zonation scheme based on the two groups which possesses high resolution (<500,000 years) in pa ticular intervals. This zonation holds great promise for furthering investigations of Cretaceous paleoenvironmental and paleoceanographic problems.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.